Optical disks may generally be used as removable media for retrieving and storing digital information, e.g. data, audio and video. Optical discs may be classified into disk types according to disk generations into Compact Disc (CD), Digital Versatile Disc (DVD) and Blu-Ray Disc (BD). Optical discs may further or alternatively be classified into read-only (ROM), recordable (R) and rewritable (RW, RE, RAM). Currently trends include miniaturizing a spot diameter using a high numerical aperture (NA) objective lens and using increasingly shorter wavelength light sources.
An optical disk drive may be arranged to handle optical disks of multiple generations. An optical disk drive may e.g. be arranged to read and write CD-generation disks, DVD-generation disks as well as BD-generation disks. An optical disk drive may alternatively be arranged to e.g. read CD-generation disks and read and write DVD-generation disks, while not being capable of scanning BD-generation disks. Such optical disk drive will reject a BD-generation disk.
Each disk generation may require operation conditions specific for the disk generation. E.g., an optical disk drive may be arranged to scan (read and/or write) a CD-generation disk with a infrared focussing spot using an infrared laser at a numerical aperture of e.g. 0.50 of an objective lens, a DVD-generation disk with a red focussing spot using a red laser at a numerical aperture of e.g. 0.65, and a BD-generation disk with a blue focussing spot using a blue-violet laser at a numerical aperture of e.g. 0.85. Additionally, other operation conditions, such as e.g. scanning velocity, may depend on the disk generation or on the disk type in general.
In starting-up of the optical disk drive, e.g. after loading a new optical disk drive or after powering-on of the optical disk drive, the optical disk drive may thus be arranged for determining a disk type of the optical disk loaded in the optical disk drive. This starting-up may consumer considerable time, referred to as startup time, and may e.g. take several seconds in current prior art optical disk drives.
In determining the disk type, prior art optical disk drives may be arranged to determine the disk generation of an optical disk in the optical disk drive using a measurement of a substrate thickness of the optical disk: CD-generation disks, DVD-generation disks and BD-generation disks have a different substrate thickness, i.e. of approximately 1.1-1.2 mm, 0.6 mm and 0.1 mm respectively.
Known optical disk drives using known methods to determine the disk generation may require a considerable time for the measurement of the substrate thickness, resulting in a considerable startup time.